Xiaobaitu and other guru: What is additional system checks

Hi, few days ago, I post here that congressman office notice me that INS told them that they need 30 days to find out why my case is not approved.
Today, I received a mail which is responding to my inquiry from 800 number on Oct 4. It says:
Your I-485 application is still pending review and undergoing additional system checks. Please allow 60 days for this process to be completed before inquiring in reference to the status of this case. You will be notified by mail once a decision has been made on your case. Your patience and cooperation is appreciated.

What is additional system check? Is it same as FBI name check? It says allow 60 days for this process to be completed, does it mean the process is more predictable in terms how long it will take than FBI name check?

Thanks again for your inputs.